An assessment on the use of the debye-hückel equation for the thermodynamic modeling of aqueous systems containing polymers and salts

Abstract

-In this work, a study on the role of the long-range term of excess Gibbs energy models in the modeling of aqueous systems containing polymers and salts is presented. Four different approaches on how to account for the presence of polymer in the long-range term were considered, and simulations were conducted considering aqueous solutions of three different salts. The analysis of water activity curves showed that, in all cases, a liquid-phase separation may be introduced by the sole presence of the polymer in the long-range term, regardless of how it is taken into account. The results lead to the conclusion that there is no single exact solution for this problem, and that any kind of approach may introduce inconsistencies.

Colloidal Systems in Concentrated Electrolyte Solutions Exhibit Re-entrant Long-Range Electrostatic Interactions due to Underscreening

“…It has been argued that the linear approximation used in the Debye−Huckel theory limits its applicability to low electrolyte concentrations in the millimolar range. 14,15 However, numerous surface force measurements at concentrations up to 0.1 M find that the decay in the interparticle force or the interaction energy between surfaces is in agreement with the Debye length. 16−20 Also, it is well argued on theoretical grounds, that linearization of the nonlinear Poisson−Boltzmann equation introduces only minor errors, and hence, the Debye−Huckel theory is applicable up to concentrations of ∼1 M for 1:1 electrolytes.…”

“…The Debye length decreases with an increase in salt concentration and is assumed to be independent of the type of ion other than through the valency. It has been argued that the linear approximation used in the Debye–Hückel theory limits its applicability to low electrolyte concentrations in the millimolar range. , However, numerous surface force measurements at concentrations up to 0.1 M find that the decay in the interparticle force or the interaction energy between surfaces is in agreement with the Debye length. − Also, it is well argued on theoretical grounds, that linearization of the nonlinear Poisson–Boltzmann equation introduces only minor errors, and hence, the Debye–Hückel theory is applicable up to concentrations of ∼1 M for 1:1 electrolytes . Ultimately, however, the applicability of the theory must break down at high concentrations as the granularity of the solvent and the finite size of the ions becomes important when the distance between ions is small.…”